1. Field of Invention
The present invention relates to a bump fabrication process. More particularly, the present invention relates to a bump fabrication process capable of producing a bump having a larger size and height.
2. Description of Related Art
In the fabrication of integrated circuit packages, a chip is linked to a carrier inside a first level package in one of three ways including wire bonding, tape automatic bonding (TAB) and flip chip (F/C). In a tape automatic bonding or a flip chip package, the process of linking up the chip and the carrier involves the production of bumps on the bonding pads of the chip. In fact, the bump serves as an electrical medium for connecting the chip and the carrier. A variety of types of bumps have been developed such as solder bumps, gold bumps, conductive polymer bumps and polymer bumps. However, solder bumps are the most popular type.
FIGS. 1A to 1F are schematic cross-sectional views showing the progression of steps for forming a conventional solder bump. As shown in FIG. 1A, a wafer 110 having an active surface 112 with a passivation layer 114 and a plurality of bonding pads 116 (only one is shown) is provided. The passivation layer 114 exposes the bonding pad 116 on the active surface 112 of the wafer 110. As shown in FIG. 1B, an under-ball-metallurgy (UBM) layer 120 is formed over the active surface 112 of the wafer 110 by carrying out one of the processes including evaporation, sputtering and electroplating. As shown in FIG. 1C, a relatively thick patterned photoresist photoresistant layer 130 is formed over the active surface 112 of the wafer 110. The patterned photoresist photoresistant layer 130 has a plurality of openings 132 (only one is shown) each one exposing a portion of the under-ball-metallurgy layer 120.
As shown in FIG. 1D, solder material 140 is deposited into the cavity space bounded by the sidewalls of the opening 132 and the under-ball-metallurgy layer 120 by carrying out one of the processes including evaporation, electroplating and printing. As shown in FIG. 1E, the thick photoresist photoresistant layer 130 is removed. Using the solder block 140 as a mask, a portion of the under-ball-metallurgy layer 120 outside the solder block 140 is removed so that only a portion of the under-ball-metallurgy layer 120 underneath the solder block 140 is retained. As shown in FIG. 1F, a reflow process is conducted so that the solder block 140 is transformed into a solder bump 142 having a spherical shape.
In order to increase height level of the solder bump 142, diameter of the opening 132 in the photoresist photoresistant layer 130 or thickness of the photoresist photoresistant layer 130 is often increased. Hence, more solder material 140 is able to accumulate inside the opening 132 and a solder bump 142 having a higher height level is ultimately produced after the reflow process. However, if the thickness of the photoresist photoresistant layer 130 is intended to be increased, it needs to precisely control the processes of exposure and development. In this situation, the process for fabricating the solder bump 142 is even more complicated, making completion of the processes not easy to perform.